1. Field of the Invention
The present invention relates to a novel capacitor structure and a method of using the capacitor structure in a semiconductor device. More particularly, the present invention is directed to a novel capacitor structure with substantially improved capacitance, increased high frequency capacitance stability, reduced leakage and smaller charge trapping, and a method of using the capacitor structure with a bilayer working electrode in a semiconductor device.
2. Description of the Prior Art
MIM (Metal-Insulator-Metal) capacitors are essential passive components for use in a wide variety of electronic devices. For example, electronic applications such as Dynamic random access memory (DRAM), analog integrated circuits, and radio frequency (RF) circuits all may have one or more MIM (Metal-Insulator-Metal) capacitors.
Dynamic random access memory (DRAM) is a semiconductor device which includes at least one transistor and one capacitor. In order to improve the capacitance of the capacitor and the possibility to downscale the dimensions of the dynamic random access memory, it is critical to increase the capacitance and other electric properties of the capacitors. Further, some additional properties of the capacitors, such as high frequency capacitance stability, leakage and inverse hysteresis should be improved as well.
As the technology advances, the demand for larger capacitance density has become higher in order to facilitate the shrinkage of the devices and to reduce the production cost. To meet this demand, there are many theoretical possibilities. For example, candidate materials of higher dielectric constant (high-k) may serve as the dielectric layer disposed between the top electrode and the bottom electrode. Suitable materials may be Hfo2, ZrO2, Ta2O5, Nb2O5, or SrTiO3.
Another possible way to increase the capacitance of the capacitors is to reduce the thickness of the dielectric layer. However, there is a physical limit when reducing the thickness of the dielectric layer because a capacitor with an insufficient thickness often fails due to lack of reliability.
Although ruthenium metal is considered as a prospective electrode material for use in gate stacks in view of its higher work function, lower resistivity, and ease of patterning via dry etch, this material is often associated with an undesirable decrease in capacitance, namely capacitance loss in terms of increase in EOT (equivalent oxide thickness). Also, for a capacitor for use in a high frequency capacitance purpose, the capacitance needs to be stable at high frequency.
As a result, there is still a need to have a novel capacitor structure with a substantially better capacitance, increased high frequency capacitance stability, reduced leakage and smaller inverse hysteresis for use in different challenging purposes.